ppp0 and it's txqueuelen with HSDPA gsm modems

ppp0 and it's txqueuelen with HSDPA gsm modems

[Jar]

Hello

What would be "optimal" value for ppp0 device's txqueuelen, when it is 
used with HSDPA gsm modem for link which downlink speed is 1Mbit/s and 
uplink speed is 384kbit/s and ping ~80..100 ms? Is the default value 3 
just OK?

-- 
Best Regards, Jar

RE: ppp0 and it's txqueuelen with HSDPA gsm modems

[Lie Arne]

> -----Original Message-----
> From: linux-ppp-owner@vger.kernel.org 
> [mailto:linux-ppp-owner@vger.kernel.org] On Behalf Of Jar
> Sent: 21. oktober 2008 20:44
> To: linux-ppp@vger.kernel.org
> Subject: ppp0 and it's txqueuelen with HSDPA gsm modems
> 
> Hello
> 
> What would be "optimal" value for ppp0 device's txqueuelen, 
> when it is used with HSDPA gsm modem for link which downlink 
> speed is 1Mbit/s and uplink speed is 384kbit/s and ping 
> ~80..100 ms? Is the default value 3 just OK?
> 
> --
> Best Regards, Jar
Jar,

I would suggest using normal TCP calculation, i.e. that you dimension
the txqueue size after the "BDP rule": bandwidth x delay product. Using
your outbound numbers this is:
1,000,000 x 0.1 = 100,000 bits = 12,500 bytes. Assuming 1500 byte
packets, this is txqueue = 12,500 / 1500 = 8.3 packets. So you could try
txqueue size in the region 8-10, this should prevent queue starvation at
packet drop events caused by traffic overload, even if you only have one
single TCP flow.

Best regards,

Arne Lie
SINTEF ICT, Dept. of Communication Systems
e-mail: arne.lie@sintef.no 

Re: ppp0 and it's txqueuelen with HSDPA gsm modems

[Jar]

Lie Arne wrote:
>> What would be "optimal" value for ppp0 device's txqueuelen, 
>> when it is used with HSDPA gsm modem for link which downlink 
>> speed is 1Mbit/s and uplink speed is 384kbit/s and ping 
>> ~80..100 ms? Is the default value 3 just OK?
>>
>> --
>> Best Regards, Jar
> 
> I would suggest using normal TCP calculation, i.e. that you dimension
> the txqueue size after the "BDP rule": bandwidth x delay product. Using
> your outbound numbers this is:
> 1,000,000 x 0.1 = 100,000 bits = 12,500 bytes. Assuming 1500 byte
> packets, this is txqueue = 12,500 / 1500 = 8.3 packets. So you could try
> txqueue size in the region 8-10, this should prevent queue starvation at
> packet drop events caused by traffic overload, even if you only have one
> single TCP flow.

OK, thanks. But is txqueuelen for transmit data only and then the 
downlink value (384kbit/s) should be used in the calculation? With 
384kbit/s the txqueuelen would be 3.2 which is quite same as ppp0 default 3.

-- 
Best Regards, Jar